Maternal Birth Grandmother and Birth Siblings need advice on Open Adoption

I hope I have found a source to help me answer this dilemma. I am a maternal birthmom Grandparent. My daughter after 30 days in the hospital with 3rd birth child, giving her much maternal love and care, ( according to nurses records) was unable to particiapte any further and walked away from the hospital , after she was told baby would be apprehended. My daughter was a known addict. I am raising her 2 beautiful and older children , 14 and 7. The ministry at 6 weeks of age of the baby, contacted me to tell me of the baby's birth. They Asked if I would take a third. I said No, this baby must be given a chance for her own family and a " NORMAL " life. I told them I wanted her placed for adoption. 3 months later , after I finally located my daughter she was notified baby would go for adoption. My daughter , through her pain, did not / could not step forward , and it was left to me , to provide child's history to the best of my knowledge.(Father unknown ). At 5 months baby had no potential family. I finally was able to refer a couple I knew , through my grandson's school, as prospective parents. The Social Workers moved on it, my friends moved to a different part of the city as their 2 older children went to school with my youngest grandchild. The prospective parents, received the baby on her first birthday. At the beginning of the discussions, we established this would be their baby, and the grandparents would be the adoptive grandparents. I, in the back of my mind, thought , we may have some contact , but did not expect it to be overwhelmingly in favor of an open adoption as such. The Adoptive parents , have now told me how my 14 yr old grandaughter would be such a positive role model for their daughter. They adore my other grandkids, and want them involved as siblings to their child. My grandson and their twin boys are ecstatic that they will have a life long special relationship. Here is the problem. My son who is 2 yrs older than his sister, lives a distance from us, and is adamant that we not be involved in this child's life, and that we let go, so she never learns about her birth mother, or that my daughter shows up years from now. My daughter by the way , does not attempt to impose herself upon her children, she realizes her life is one they should not be exposed to. She stays in touch with me, and I often look for her, so I may continually reach out, tell her there is another path, and I wil be waiting for her. My daughter knows the family is one I know, she knows I will not tell her who they are. She asked me if they were good people, and I told her baby will be well loved, will have 2 brothers, and some contact with us, and she will live an advantageous life. I told her , the adoptive parents pray for her recovery, and that one day , if she has had many years of sobriety there MAY( no promise) be an opportunity to meet them and the child. I told her , I will ensure she has a picture of the little one yearly, as provided to me by AD parents. Now to the issue at hand. The AD parents wish to make the birth siblings and myself extended family. They will be her brother and sister , in addition to her adoptive brothers. I am to be considered Nana. My 14 yr old grandaughter and I , question and worry , this will not be healthy for the little one in establishing her new family. We do not want her to ever think her AD family is not her real family. We don't know how we will handle the questions re: her birthmom , as her life is not one we want her to know about. This is my concern... My 14 yr old grandaughter and I , do not want this little one growing up , knowing anything about the difficulties, her birthmom experienced in her late teens and adult life. My son and all my friends ( including adult adoptees in this ) are adamant that we need to stay away , and not be involved in an open adoption, for the sake of the child. My friends also think this is a continual reminder to the older siblings also , of their mother's lifestyle that is particularily painfiul for us . My grandson has been with me since birth , and at 7 has not given much thought to my daughter's lifestyle, and embraces me as Mom. My grandaughter on the other hand, has never had a year where her mother's life has not caused her sadness. My grandaughter is confused as to what to do. She on one hand will say , this is a reminder of all the things my brother and I have never and will never have, a reminder of another little piece of me that is missing. And yet her face lights up when she sees the baby . What am I do to do here? There are 3 children involved. I have to make the right decision for ALL of them ! My son is angry with me, and will probably cut me out of his life , If I embrace the OA. If I do embrace it , I will never be able to share anything with him , about the latest baby . My grandaughter and I , love the baby , and want to make the right decision for her, excluding our own feelings. Keep in mind there could be many babies to come. My grandson and this baby , had it not been for the illecit drugs, very possibly would have been terminated. There have been many terminations, and I am praying my daughter, will be able to find the consciouness and awareness to get her tubes tied. So far her two youngest at risk births children have dodged major bullets , and appear to be healthy . The 7 yr old has minor learning issues but we are winning that battle. The baby is ahead of all mile stones, and healthy after a rocky start. She was in foster care, until adopted at one year old. Please tell me what you feel !